Latch trip switch



. INVENTOR. WILBERT A. MARTIN ,q ATTORNEY United states Patent Q rarcn 'rnrr swrrorr Wilbert Martin, Freeport, 111., assignor to Minneapolis.- l-loncywo l Regulator Company, ltllinneapolis, Minn, a corporation of Delaware Application .inne 311, 1952, Serial No. 2965M 2 @lairns. (ct. zen-44 This invention relates to the mechanism to operate an electric switch having latch trip snap action in at least one direction. The switch was developed specifically as a propeller pitch limit for aircraft to cut the power to the propeller pitch changing motor when the blades have rotated to the appropriate limit. The switch is mounted in the propeller hub and rotates with the propeller in a position such that the vertical axis of the switch as shown in the drawing lies along a radius from the axis of rotation. The switch is, therefore, subject to great centrifugal force and to. extreme vibration. Such a switch must be as near perfect as possible to avoid damageto the aircraft and possible injury or death of occupants.

Objects of this invention are to provide a switch the parts of which are statically balanced against actuation by centrifugal force, to provide a switch operable to break circuit with snap action, to provide a switch in which Contact force is maintained up to the time the contacts open, to provide a switch in which the contacts are held closed by a latch until the switch is operated, to provide a switch operable to break a plurality of circuits substantially simultaneously, to provide a switch in which the contacts are readily accessible for examination, to provide a switch in which the movable contacts may be easily replaced, to provide a switchhaving the mechanical portion separated from the electrical portion, to provide a switch in which the mechanical parts are readily accessible, to provide a switch that is positively operated even though the springs in it are broken, to provide a switch operable by cams moving in either of two directions, and to provide a switch that is rugged in construction.

In the drawings:

Fig. l is an elevation of the switch partially broken away with the cover over the mechanical portion removed, showing the normal position of the parts,

Fig. 2 is a sectional view along line 2-2 in Fig. 1

Fig. 3 is a fragmentary view similar to Fig. .1 showing the position of the mechanical portions just before the contacts are snapped open, v

. Fig. 4 is a fragmentary view similar to Figs.,l and 3 showing the position of both mechanical and electrical portions when the switch is operated and fully overtraveled, and

Fig. 5 is a fragmentary view showing the operation when one of the springs is broken.

In the preferred embodiment shown in the drawings, the housing 1, made of insulating material, serves as a support for the mechanism as well as an enclosure. It has a cavity 2 from one side enclosing the operating mechanism and a cavity 3 from the other side enclosing the electrical mechanism, the cavities being interconnected by an opening 4. A mounting bracket 5 is fastened to the housing. A shaft 6 passes through a wall of cavity 2 and is pivotally supported thereon. An actuator 7 having a cam surface 8 and a counterweight 9 is fixed on the external end of shaft 6. A yoke 10, comprising arms 11 and 12, is rigidly attached to the end of the shaft 6. A roller 13 is pivoted on the end of arm 12, while a hammer 14 is formed at the end of arm 11. The actuator 7, counterweight 9 and yoke are statically balanced to eliminate the effects of centrifugal force upon the switch.

A contact carrier 15 made of insulating material pivots on screw 16 in cavity 3. The contact carrier is provided with a lever 17 which extends upwardly Zfifildfi Fatenteti Dec. 14, 1954 through opening 4 and between roller 13 and hammer 14 so asto bemovable thereby. Shorting bars 18 and 19 are so mounted on opposite ends of the carrier 15 astobe biased. away from the contact carrier 15. A stationary contact 20 is connected by a conducting strap 21 to terminal22 extending through the bottom of the housing and a second stationary contact 23'is connected by a conducting strap 24,to aterminal 25 passing through the back wall of the housing are positioned tobe shorted by bar 18 to close one electriocircuit, while stationary contact 26 connected by strap 27 to terminal 28 extending through the bottom of the housing and a fourth stationary contact 29 connected by conducting strap 36 to a terminal (not shown) passing through the back wall of the housing are positioned to be shorted by bar 19 to close another electric circuit.

A latch 31 pivoted to the housing on bearing 32 is counterbalanced against centrifugal force and biased intothe path. of motion of lever 17 and against roller 13 by a compression spring 33 acting between the upper wall of cavity 2 and the latch 31. A compression spring 34 acting between arm 11 and lever 17 serves to bias the lever toward the roller 13 and into contact with latch 31 when the latter is in the path of motion of the lever 17. A third compression spring 35 biases the actuator 7 in a clockwise direction as shown in, the drawing, Covers over the cavities 2 and 3 may be provided to complete the enclosure of the switch mechanism.

,Operation of the switch may be accomplished by moving actuator 7 in a counter-clockwise direction. Force may be applied to, actuator 7 by a cam 36 moving in, the direction of-the arrow in Fig. 3, or it may be applied by a sloping cam 37 moving, in the opposite direction against cam surface 8 which is shaped to cause the actuator 7 to move counter-clockwise. Counter-clockwise rotation of actuator 7 compresses spring 35 and rotates shaft 6 carrying yoke 10 in a clockwise manner also. Movement of theyoke 10 compresses spring 34, pressing lever 17 against latch 31 until the parts reach the position shown in Fig. 3. Further movement of the yoke causesthe roller 13 to lift latch 31 from the path of movement of lever 17 permitting the compressed spring 34 to move the lever 17 with snap action to the position shown in Fig. 4. Contact carrier 15 which is rigid with lever.17 is thus caused to quickly break the circuits from terminal 22 through shorting bar .18 to terminal 25 and from terminal 28 through shorting bar. 19 to the fourth terminal which is not shown in the drawing.

1 Upon removal of the operating force from actuator 7, spring 35 moves actuator 7 and with it shaft 6 and yoke 10 back to its initial position. This movement of yoke 10 causes the roller 13 to move lever 17 beyond the end of latch 31 which thereupon is moved into latchingposition by compression spring 33. Contact car rier lS moved by lever 17 to reclosethe circuits from terminal 22, through shorting bar 18, to terminal 25 and from terminal 28 through shorting bar 19 to the fourth terminal which is not shown.

In a construction of this type produced by mass production, it is essential that all parts be interchangeable. In order to accommodate the resulting tolerances, it is necessary that lever 17 be returned beyond the end of latch 31. This would be impossible without resilient mounting of at least one contact in each circuit. There is nothing novel in this type of contact mounting and it may be accomplished in many difierent ways, but for convenience it is the shorting bars 18 and 19 which have been resiliently mounted. This resilient mounting has also made practical the making and breaking of two circuits by this type of operating mechanism.

This mechanism has many advantages over prior mechanisms of this sort. For example, if spring 34 should break, the contacts would be held closed as before breakage by roller 13 and latch 31. When the switch is operated, movement of actuator 7 causes roller 13 to lift the latch 31 from the path of motion of lever 17. At the time that the latch 31 is lifted from the path of the lever 17 the hammer 14 is very close to the lever 17 so that very little additional motion of the actuator is requiredfor the hammer 14 to engage lever 17 as shown in Fig. 5 and positively drive it to break the circuits. When the operating force is removed from the actuator 7, it is returned by spring 35 to its initial position. The roller 13 engages lever 17 and moves it back to latched position. It will be seen that the circuits are opened a little later and without snap action, but they are opened within a safe position of the actuator 7. The closing is the same as before.

If spring 33 breaks permitting the latch 31 to move from the path of motion of lever 17, spring 34 presses lever 17 against the roller 13 at all times so that the lever moves as though operated by the roller. This results in somewhat earlier opening of the circuits but Without snap action and no difference in closing the circuits.

If both springs 33 and 34 are broken, the roller 13 holds lever 17 in circuit closing position until operating force is applied to the actuator 7. Movement of actuator 7 causes hammer 14 to'engage lever 17 and move it to circuit opening position without snap action. Removal of the operating force permits the spring 35 to move actuator 7 back to its initial position and causes roller 13 to return lever 17 to circuit closing position. The opening of the circuits will be a little later and without snap action. There is no change in circuit closing.

Breakage of spring 35 will permit normal circuit opening operation, and by making the effective mass of the counterweight 9 such as to provide some clockwise force on the pivotally associated parts due to centigfugal force, a circuit closing force will also be availa le.

With any of these modes of operation, if the contacts stick due to welding or for any other cause, the circuits are broken when the hammer 14 engages the lever 17 and positively drives it from circuit closing position. Further separation of the contacts may or may not be with snap action depending on the mode of operation. Breaking circuit by positive drive takes place a little later than by normal snap action.

Inspection of all mechanical parts may be made by removal of the cover over cavity 2. Springs are readily accessible so that they may be replaced if. necessary. Inspection of all electrical parts may be made by removal of the cover over cavity 3. The contacts may be more closely examined by removing screw 16 and taking contact carrier 15 with its associated shorting bars 18 and 19 from the cavity 3. If desired, these parts can be replaced.

I claim:

1. An electric switch comprising a housing, a stationary contact on said housing, a member pivoted in said housing and carrying a movable contact cooperat-- ing with said stationary contact, an arm on said member extending radially from the pivotal axis, an actuator pivotally mounted in said housing on an axis parallel to the axis of said member, a roller on said actuator rotatable on an axis parallel to the pivotal axis of said actuator and adapted to engage said arm to move said member to contact closed position, a spring biasing said actuator in a direction to close said contacts, a second spring acting between said actuator and said arm and biasing said arm toward said roller, a latch pivoted in said housing on an axis parallel to the axis of said actuator and having a surface adapted to engage said roller, a third spring biasing said latch toward said roller, said latch having a portion adapted to engage said arm when in closed circuit position to prevent separation of said contacts, and said latch being movable by said roller to a position out of engagement with said arm on movement of said actuator to separate said roller from said arm, such movement of said actuator increasing the bias of' said second spring tending to move said arm in a direction to open said contacts until said arm is released by said latch, said roller acting as a stop for said arm when moved by said second spring to open said contacts.

2. An electric switch comprising a housing, a stationary contact on said housing, a member pivoted in said housing and carrying a movable contact cooperating with said stationary contact, an arm on said member extending radially from the pivotal axis, an actuator pivotally mounted in said housing on an axis parallel to the axis of said member, a roller on said actuator rotatable on an axis parallel to the pivotal axis of said actuator and adapted to engage said arm to move said member to contact closed position, a spring biasing said actuator in a direction to close said contacts, a second spring acting between said actuator and said arm and biasing said arm toward said roller, a latch pivoted in said housing on an axis parallel to the axis of said actuator and having a surface adapted to engage said roller, a third spring biasing said latch toward said roller, said latch having a portion adapted to engage said arm when in closed circuit position to prevent separation of said contacts, and said latch being movable by said roller to a position out of engagement with said arm on movement of said actuator to separate said roller from said arm, such movement of said actuator increasing the bias of said second spring tending to move said arm in a direction to open said contacts until said arm is released by said latch, said roller acting as a stop for said arm when moved by said second spring to open said contacts, and said actuator having a portion adapted to engage the side of said arm opposite said roller when said latch is out of engagement with said arm and said arm remains in contact closed position.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,894,074 Von Normann Jan. 10, 1933 2,073,319 Rosay Mar. 9, 1937 2,352,815 Van Valkenburg July 4, 1944 2,461,707 Szerlip et al. Feb. 15, 1949 2,468,551 Goff Apr. 26, 1949 2,523,370 Jeffrey Sept. 26, 1950 2,586,075 Miller Feb. 19, 1952 2,604,792 Jeffrey July 29, 1952 

